There is inadequate evidence for the carcinogenicity of cobalt and cobalt compounds in humans. Consequently, the International Agency for Research on Cancer (IARC) has evaluated cobalt metal without tungsten carbide as possibly carcinogenic to humans (Group 2B). The aim of the study was to assess the risk of cancer among workers employed in a Finnish cobalt plant since the beginning of production in 1968.
The study cohort consisted of all males employed by the Finnish cobalt plant for at least a year during 1968-2004. The follow-up for cancer was performed by studying the files of the Finnish Cancer Registry, using personal identity codes as a key. The cohort was divided into subcohorts by exposure levels. Standardised incidence ratios (SIRs) and 95% confidence intervals (95% CIs) were calculated as ratios of the observed numbers of cancer cases and the numbers expected on the basis of incidence rates in the population of the same region.
The follow-up cohort consisted of 995 men with 26,083 person-years. During the follow-up period, 92 cases of cancer were diagnosed (SIR 1.00, 95% CI 0.81-1.22), six of which were lung cancer cases (SIR 0.50; 95% CI 0.18-1.08). The only cancer type with increased incidence was tongue cancer (three cases, SIR 7.39; 95% CI 1.52-21.6). We observed no dose-response effect across the different exposure levels and the incidence of any cancer type.
The results suggest that occupational exposure to cobalt is not associated with an increased overall cancer risk or lung cancer risk among cobalt workers. Because of the small number of cancer cases the results must be interpreted with caution.
A recent Danish study showed that the prevalence of nickel allergy decreased among young female patients and increased among older female patients with dermatitis patch tested between 1985 and 2007 at Gentofte Hospital, Denmark. The prevalence of cobalt allergy remained unchanged.
To examine fluctuations in the prevalence of nickel and cobalt allergy after implementation of the nickel regulation, by analysing patch test results from male and female patients with dermatitis tested between 1992 and 2009 at Odense University Hospital, Denmark.
A retrospective analysis of patch test data was performed (female, n = 5821; male, n = 3317). Comparisons were made using the chi-square test for trend. Logistic regression analyses were used to test for associations.
The prevalence of nickel allergy decreased significantly among the 2-30-year-old female patients, from 29.8% in 1992-1997 to 19.6% in 2004-2009 (p 60-year-old female patients. The overall prevalence of cobalt allergy increased significantly, from 3.7% in 1992-1997 to 5.1% in 2004-2009 (p = 0.03). The overall prevalence of nickel and cobalt allergy among male patients during the test period was 5.2% and 2.2%, respectively, and no significant change across the test years was detected.
The prevalence of nickel allergy decreased among young female patients and increased among older female patients with dermatitis, probably because of a cohort effect. The overall prevalence of cobalt allergy increased from 1992 to 2009. No significant trend in the prevalence of nickel and cobalt allergy among male patients was found.
This study is part of the EURO-TERVIHT project (Trace Element Reference Values in Human Tissues) which aims at establishing reference intervals for trace elements in blood, urine and other human tissues. In this study reference intervals (0.05-0.95 fractiles) were estimated for lead in blood (105-529 nmol/l for men, 80-340 nmol/l for women), manganese in blood (100-271 nmol/l) and arsenic in urine (36-541 nmol/l for men, 21-475 nmol/l for women). Upper reference limits (0.95 fractile) were established for chromium in urine (13 nmol/l), nickel in urine (52 nmol/l) and cobalt in urine (23 nmol/l for men, 31 nmol/l for women). The reference group was a Danish subpopulation (n = 189), age 40-70 years. The influence of gender, age, health status parameters, nutrition and various lifestyle factors was investigated. Urinary arsenic and blood lead levels were found to be higher for men than for women. Arsenic levels also increased with age up to 60 years, and then decreased. Alcohol intake lead to increased arsenic levels in urine as well as blood lead levels. Urinary nickel levels were higher in persons frequently eating porridge and porridge oats.